1. Field of the Invention
This invention relates to a digital vector generator system for graphic displays and more particularly to such a system having three visual characteristic vector generators operating synchronously with spatial vector generators to generate multi-dimensional visual characteristic vectors.
2. Discussion of the Prior Art
Graphical image display systems provide an array of discrete points known as pixels at which emitted light intensities may be independently controlled. Each pixel may represent a single intensity for a monochrome system or three different primary color intensities for a three color system.
A display is generated by effectively sampling light intensities at each point of a source image which corresponds to a display pixel and then illuminating each pixel in accordance with its corresponding sampled light intensity value. In the case of a computer generated image the pixel light intensity values are generated by a computer as a prediction of what the values would be if sampled from an actual image of a selected object under selected light conditions.
Raster scan display systems typically provide a two dimensional rectangular array of pixels arranged in rows and columns. A frame buffer stores intensity values for each pixel in a location which may be addressably accessed in response to the row and column position of the pixel within the array. As a controlled beam scans the pixel array row by row, the corresponding illumination data is read from the frame buffer and used to control the intensity of the scanning beam at each pixel and hence the corresponding illumination intensity of the pixel.
Video image data is typically provided to a digital vector generator as lists of lines or polygons defined by end points and corners or line slopes. Visual characteristic information is provided for each line or polygon as part of the test. The spatial information is utilized to initialize digital vector generators which then proceed to generate spatial address locations which define each line of a display as a plurality of adjacent pixel points. The vector generators generate address information defining X, Y and Z coordinates which locate the line in three dimensional display space.
A frame buffer store is provided having an address location corresponding to each pixel location in a display image. Visual characteristic information defining the visual display characteristics of each pixel must be stored at the address corresponding to the pixel. The visual characteristic information may have different portions defining intensity and hue, may have different portions defining Red, Green and Blue (RGB) color intensities, or may have information which is to address a color map table to produce the desired visual characteristic information.
While the digital vector generator determines the X, Y and Z coordinates for a next point on a line, a central processing unit must also determines the visual characteristic information for the next point. When both the visual characteristic information and spatial address information are available, the spatial address information is used to address the frame buffer and the visual characteristic information is written into the selected address location.
Because of the large number of pixels which comprise a video display, for example, 768.times.525=403,200, a considerable period of time may be required to generate all of the pixel data for a display image. Several minutes may be required to generate an image using sophisticated shading algorithms such as Phong shading or Gouraud shading. Various shading and texturizing techniques are described in the following references.
Smith, Alvy Ray, "Tint Fill", Computer Graphics, (ACM) Vol. 13, No. 2, pp. 276-283 (August, 1979), discloses an algorithm for filling a bounded area. The algorithm is specially adapted to handle graduated shading at line edges which is said to be introduced by all antialiasing techniques.
U.S. Pat. No. 4,225,861, "Method and Means for Texture Display in Raster Scanned Color Graphic System", Langdon, Jr. et al, discloses a graphic system including a color map table and a texture RAM which is capable of producing a texturized surface. However, the disclosed system does not provide the broad range of selectable operating modes that are available with the present arrangement.
A Single dimension vector generator is disclosed in U.S. Pat. No. 3,996,585 to Hogan et al. Integer steps are assumed in the vertical direction while the generator produces horizontal dimension pixel data. A Z dimension cannot be accommodated and the vector generator is used only for spatial information, not color intensity information.
U.S. Pat. No. 4,212,009, "Smoothing a Raster Display", Adleman et al teach an arrangement in which the width of the raster beam is varied in accordance with the data being displayed.